Kiwifruit SVP2 gene prevents premature budbreak during dormancy

MADS-box genes similar to Arabidopsis thaliana SHORT VEGETATIVE PHASE (SVP) have been implicated in regulation of flowering in annual species and winter dormancy in perennial species. However, the underlying regulatory mechanisms remain to be identified. In this study, the role of kiwifruit SVP2 was explored using ectopic transgenic expression in kiwifruit species with different chilling requirements and the model species tobacco, followed by transcriptomic analysis of transgenic kiwifruit plants. Ectopic expression of SVP2 affected the duration of dormancy in a high-chill kiwifruit Actinidia deliciosa. This effect could be overcome by sufficient winter chilling. SVP2 had a minimal effect on the duration of dormancy in a low-chill kiwifruit A. eriantha. Expression in a tobacco cultivar with photo-periodic regulation of flowering resulted in retarded vegetative growth but no impact on flowering. Transcriptomic analyses of the kiwifruit SVP2 transgenic and control lines identified 92 significantly differentially expressed genes potentially involved in SVP2-mediated growth repression during dormancy, suggesting a role complementary to abscisic acid (ABA). This study has demonstrated that kiwifruit SVP2 has an integrative role in suppression of meristem activity to prevent precocious budbreak before the fulfilment of winter chilling requirements.